The inuence of type and concentration of stabilisers on the thermal stability of plasticised poly (vinyl chloride) M. Davallo* Department of Chemistry, North Tehran Branch, Islamic Azad University, Tehran, Iran. Recieved: June 2011, Revised: July 2011, Accepted: August 2011 Abstract: The inuence of a variety of stabilisers and its content on the thermal stability of plasticised poly (vinyl chloride), PPVC were investigated. Experimental results indicated that the type of stabilliser had a signicant inuence on the thermal stability of PPVC. However, after identifying the order of efciency of the thermal stability of stabilisers added to PVC, it was found that addition of stabiliser and the amount of it can increase the thermal resistance of PPVC polymer. Keywords: Thermal stability, Poly (vinyl chloride), Thermal degradation of PVC, Decomposition of PVC. Introduction Despite of the versatility afforded from the excellent range of properties which are of- fered by plasticised poly (vinyl chloride), PPVC, major problem associated with this polymer is its instability to temperature and to photo-initiated chemical changes by the evolution of hydrochloride acid (HCl) fol- lowed by oxidation. On decomposition process, the presence of evolved HCl gas worsens the consequences of the chemi- cal reaction. HCl is a toxic product which has tendency to attack the surface of lower- grade steel tools in processing equipment. Formation of polyene (C=C) sequences during dehyrochlorination leads to progres- sive compound when degraded excessively. However, it has been recently proposed that *Corresponding author E-mail: [email protected]90 ، ﺗﺎﺑﺴﺘﺎن2 ﺳﺎل ﭘﻨﺠﻢ، ﺷﻤﺎره
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The inuence of type and concentration of stabilisers on thethermal stability of plasticised poly (vinyl chloride)
M. Davallo*
Department of Chemistry, North Tehran Branch, Islamic Azad University, Tehran, Iran.
Recieved: June 2011, Revised: July 2011, Accepted: August 2011
Abstract: The inuence of a variety of stabilisers and its content on the thermal stability ofplasticised poly (vinyl chloride), PPVC were investigated. Experimental results indicatedthat the type of stabilliser had a signicant inuence on the thermal stability of PPVC.However, after identifying the order of efciency of the thermal stability of stabilisers addedto PVC, it was found that addition of stabiliser and the amount of it can increase the thermalresistance of PPVC polymer.
Keywords: Thermal stability, Poly (vinyl chloride), Thermal degradation of PVC,
Decomposition of PVC.
Introduction
Despite of the versatility afforded from the
excellent range of properties which are of-
fered by plasticised poly (vinyl chloride),
PPVC, major problem associated with this
polymer is its instability to temperature and
to photo-initiated chemical changes by the
evolution of hydrochloride acid (HCl) fol-
lowed by oxidation. On decomposition
process, the presence of evolved HCl gas
worsens the consequences of the chemi-
cal reaction. HCl is a toxic product which
has tendency to attack the surface of lower-
grade steel tools in processing equipment.
Formation of polyene (C=C) sequences
during dehyrochlorination leads to progres-
sive compound when degraded excessively.
However, it has been recently proposed that
*Corresponding author E-mail: [email protected] سال پنجم، شماره 2، تابستان
Experimental
Materials
Types of stabiliser on the thermal stability
of PPVC
The PVC used in this study is a suspen-
sion resin with solution viscosity k-value of
65 (from Arvand Petrochemical Co, Iran).
Eight different types of stabiliser (referred
to as 1, 2, 3, 4, 5, 6, 7 and 8) used in this
study which were compatible with PVC,
all were with industrial grade (from Ciba-
Geigy). The additives used are shown in
Table 1. The PVC compounds formulations
are shown in Table 2. These are based on
a dialphanyl phthalate (DAP) plasticised
formulation, (with an industrial grade), but
without the llers. All compounds wereadded with pigment.
Sample preparation
A high speed laboratory mixer (Fielder
8L) was used to mix PVC and the addi-
tives. To produce moulded at sheet, thedry compounds of PVC and additives were
rst sheeted on a two roll-mill before beingcompression moulded at the set temperature
of 160 ºC. Samples (2 cm2) for degrada-
tion testing were cut from the compressed
sheet prepared for each compound and then
were placed in a preheated oven at 180 ºC.
Samples of each compound were removed
at varying time intervals (e.g 1, 5, 10, 15,
30, 60, 120 and 180 mins) and their colour
changes were observed as a function of
time.
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the low thermal stability of PVC is due to at
least the presence of structural inhomogene-
ity in the molecules which accelerates the
rate of dehydrochlorination by activating
the carbon-chlorine (C-Cl) bonds in the sys-
tem. Thus, such structural irregularities are
thought to include initiator residue, chain
unsaturation, branches, isomer and oxida-
tion structures. The higher temperature is as-
sociated with a greater extent of degradation
and it can also be seen that a greater degree
of stabilization by increasing the concentra-
tion of stabilizer retards the development of
chain-unsaturation sequences. Degradation
of PVC due to evolution of HCl is shown by
the following mechanism:
The liberated HCl accelerates further
decomposition and if oxygen is present it
would increase the reaction and moreover it
causes both chain scission and cross-linking.
It also can accelerate the colour formation
of PVC. In this work, a variety of stabilisers
on the thermal stability of PPVC were rststudied and order of efciency of thermalstability of stabilisers were identied.Then the concentration of stabiliser which
The numbers indicates parts per 100 resin (phr) in the formulations.
The inuence of concentration of stabi-liser on the thermal stability of PPVC Af-
ter identifying the order of thermal stabil-
ity efciency of stabilisers added to PVC,samples (prepared as mentioned above)
with formulations which are shown in Table
3 were used. Samples for degradation test-
ing were cut (2 cm2) from the compressed
sheet prepared for each compound and then
were placed in a preheated oven at 180 0C.
Samples of each compound were removed
at varying time intervals (e.g 2, 10, 20, 30,
40, 80, 120 and 180 mins) and nally theircolour changes were observed as a function
of time.
(JARC) سال پنجم، شماره 2، تابستان 90نشریه پژوهش هاى کاربردى در شیمى
Table 3 PVC compounds.
Ingredient PVC1 PVC2 PVC3 PVC4 PVC5
PVC 100 100 100 100 100
DAP 50 50 50 50 50
Stabiliser
(White lead)0 1 2 4 8
Lubricant 0.5 0.5 0.5 0.5 0.5
The numbers indicate parts per 100 resin (phr) in the formulations.
tion of colour. By adding a stabiliser sys-
tem which is able to bind HCl, this in ef-
fect can retard the thermal degradation of
PPVC13,14. However, of those PPVC sam-
ples mentioned above, the PPVC that was
stabilised with white lead (PVC3) observed
to degrade slower compared to others.
The inuence of concentration of stabiliseron the thermal stability of PPVCThe thermal stability of prepared PPVCcompounds are shown in Table 5. As it canbe seen from Table 5, by increasing amountof stabiliser of PPVC, thermal stability ofPPVC is improved. Thus, colour formationduring degradation of PPVC can be sup-pressed by the amount of stabiliser added tothe polymer [13]. For example, the polymerwhich contains no stabiliser in its compo-sition degraded very rapidly in a matter ofjust a few minutes. Whereas the polymerwhich contains higher amount of stabiliser(PVC5) has better thermo-stability so hasdegraded very slowly and its colour changedto brown not black for a given time of 180mins. Hence, the order of thermal stabilityof polymers are as follows:
PVC1<PVC2<PVC3<PVC4<PVC5
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Results and Discussion
Types of stabiliser on the thermal stability
of PPVC
The thermal stability of PPVC samples
tested are shown in Table 4. As it can be
seen from Table 4, PVC2, PVC3, PVC5,
and PVC8 indicated to have better thermal
stability in comparison with other PVC.
These PVC materials degrade in slower rate
compared with those which changed colour
from clear to brown/red and nally to blackwith increasing temperature. It is proposed
اثر پایدار کننده هاى متعدد و مقدار آن در پایدارى گرمایى پلى (وینیل کلرید) نرم مورد بررسى قرار گرفت. نتایج چکیده:تجربى نشان داد که نوع پایدار کننده ها اثر قابل مالحظه اى بر پایدارى گرمایى پلى (وینیل کلرید) نرم دارد. پس از تشخیص ترتیب توانایى پایدارى گرمایى پایدار کننده ها ى افزوده شده به پلیمر، آزمایش ها نشان دادند که افزودن پایدار کننده ها و
مقدار آن مى تواند مقاومت گرمایى پلى (وینیل کلرید) نرم را افزایش دهد.